The focus of this project is on differentiation inducers as agents for improving therapeutic selectivity in cancers of lining epithelia. The first hypothesis to be tested is that differentiation-inducers act directly on tumor cells to arrest their growth and divert them toward terminal differentiation. The treatment strategy is to combine two drugs: an agent which induces differentiation of the quiescent (but proliferation-capable) cell subpopulation of the carcinoma and an anti- proliferative drug. This is based on the fact that certain tumor cells are less sensitive to certain cell-cycle arresting agents than normal cells. Three mouse epidermal cell lines which produce well-, moderately- or un-differentiated squamous cell tumors, respectively, in athymic nu/nu mice are compared to the normal parental clone as to the effect and selectively of treatments. In vitro endpoints relative to the first hypothesis are reduction in number and/or area of tumor cell colonies on plastic, and induction of differentiation-stage specific antigens. These include pemphigoid, pemphigus, certain keratins, filaggrin and a cornified envelope precursor protein. Agents found to be active in vitro are tested in vivo. The in vivo endpoints are: 1) ability to reduce growth rate or cause the regression of tumors, and 2) ability to increase the proportion of differentiating tumor cells or to induce a later stage of differentiation in tumors. The latter is detected by indirect immunofluorescence on tissue sections, direct fluorescence of dissociated cells by means of flow cytometry, or Enzyme-linked Immunosorbent assay (ELISA) of tumor tissue extracts coated in microtiter plates. Relative to the second hypothesis, agents found to protect normal epidermal cells in vitro will be tested in vivo for ability to protect lining epithelial cell targets particularly vulnerable to toxicity, including hair follicular and colon epithelium, from anti-proliferative drugs such as 1-beta-D- arabinofuranosylcytosine (Ara-C) and 5-fluorouracil. Test agents include modulators if intracellular Ca++ concentration, retinoids, Ca++- or K+- channel blockers, and modulators of protein kinase C, an enzyme involved in epidermal growth regulation. Information obtained using the mouse epidermal cell model may suggest less toxic approaches to the treatment of human cancers of keratinizing epithelia.